A system of known type for directing sheets from an input line and a second output line, used for example on sheet-collecting lines, comprises: first gripping and drawing means arranged at the input line and cooperating there-with to grip the sheets and move them, keeping them gripped, in a substantially horizontal conveying direction up to releasing them in a directing region; switching means, arranged in the directing region, activatable to deviate the sheets during their release by the first gripping and drawing means respectively along a first or a second directing direction, angularly arranged with respect to the conveying direction such as to form there-with respectively a first directing angle and a second direction angle, substantially equal but in an opposite direction to the preceding; second gripping and drawing means, operating at the first outlet line and destined to grip the sheets advancing along the first direction and drawing them in a substantially parallel direction to the conveying direction; third gripping and drawing means, operating at the second output line and inferiorly arranged to the second gripping and drawing means in order to grip the sheets advancing along the second directing line and draw them with a substantially parallel direction to the conveying direction.
The first, second and third gripping and drawing means each comprise a pair of counter-rotating rollers, first and second, arranged one above the other and on which are respectively wound a first series of upper belts and a second series of lower belts; each sheet is gripped and drawn between the horizontally developing lower branches of the second series of belts.
The switcher means comprise a deviating element in the form of a wedge which is activatable to rotate between a first position, in which it directs the sheets in release stage by the belts wound on rollers of the first gripping and drawing means towards the rollers of the second gripping and drawing means, and a second position in which it directs the sheets in release phase from the first gripping and drawing means towards the rollers of the third gripping and drawing means.
The sheet directing system further comprises: first guide means, arranged between the rollers of the first gripping means and the rollers of the second gripping and drawing means for guiding the sheets in advancement along the first orientating direction; and second guide means, arranged between the rollers of the first guide and drawing means and the rollers of the third gripping and drawing means, to guide the sheets in advancement along the second orientating direction.
In order to be correctly direction, each sheet advancing in the directing system must be gripped between the belts wound on the rollers of the second or third gripping and drawing means before it is released by the belts wound on the rollers of the first gripping and drawing means, i.e. the sheet, in order to advance in the directing system and not to snag therein, causing a shut-down, must be subjected to the constant grip on the part of the first or second or third gripping and drawing means.
The above-described directing system is therefore configured such as to direct sheets having a standard format, the dimensions of which enable them to be subjected to a constant grip on the part of the first or second or third gripping and drawing means during advancing into the directing region, and exhibits drawbacks whenever it is required to use formats having smaller dimensions to the standard format, i.e. sheets whose dimensions do not enable them to be subjected to a constant grip on the part of the first or second or third gripping and drawing means.
In this case, in order to direct the sheets correctly and prevent them from getting blocked in the directing system, it is possible to modify the configuration of the directing system according to the sheet format in use, by nearing the conveyor organs comprising the rollers of the second and third gripping and drawing means to the rollers of the first gripping and drawing means; this however requires a long set-up time due to the need to modify the reciprocal positions of the rollers of the first, second and third gripping and drawing means, and adapt the guide position.
The nearing of the conveyor organs comprising the rollers of the second and third gripping and drawing means to the conveyor organ comprising the rollers of the first gripping and drawing means determines an increase in the directing angle (first and second) and, consequently, an increase in the probability of the sheet's snagging in the directing system, positively correlated to the directing angle; in order to contain the probability of blocking within acceptable limits, it is necessary to reduce the speed of supply of the sheets, which leads to an undesirable reduction in the productivity of the directing system.
Further, the directing angle must be kept below a predetermined angle, being a directing limit, as with a greater directing angle to this limit, the probability of snagging is very high and it is not possible to contain it within acceptable limits, even by reducing the sheet supply.